Left ventricular assist devices (LVADs), originally developed as a bridge to heart transplants, are gaining wider use in long-term therapy. A critical component is the external Li-ion battery pack that powers the implanted pump through a percutaneous cable. Major drawbacks of current LVAD batteries which this project addresses, include the need for patients to carry heavy and bulky batteries, the high frequency with which batteries need recharging, and slow recharging rates. Device manufacturers employ standard, off-the-shelf batter cells that are not tailored for optimal performance under specific LVAD operation conditions; thus there is significant room for improvement in these power systems to enhance heart patient mobility and quality of life.